Gene lk is a recessive mutation which, when
homozygous, results in the very short, stout erectoides phenotype (2). Such
plants show a very much reduced response to the application of GA1,
the endogenous active gibberellin in peas, compared with Lk plants (4).
In contrast, gene lv results in an increase in internode length in plants
grown in white light and an increased response to applied GA1 (5).
This gene is thought to partially block the transduction chain from
physiologically light stable phytochrome, leading to an enhanced GA1
response and consequently increased elongation (1). Therefore it is of interest
to determine the interaction of the lk and
lvgenes and to
identify the phenotype of homozygous lklv plants. The selection
of genotype lklv may also be of use in future physiological
studies examining the control of the GA response.

These questions were examined by crossing lines NEU3
(genotype leLacrycNaLmLhLsLkLwLkaLkblv, 5) and JI1420 (leLacrycNaLmLsLhlk
LwLkaLkbLv, 2). The F1 was dwarf (5) and the F2
segregated to yield 16 erectoides and 61 non-erectoides plants (Fig. 1). The
non-erectoides group may be further divided into 44 dwarf and 17 taller plants
(Fig. 1). This separation was not pronounced. The taller plants showed
considerable variation and with two exceptions were substantially shorter than
the NEU3 parent. Likewise the dwarf progenitor of NEU3, cv Sparkle, was
substantially longer than the majority of the dwarf segregates. This appears to
have occurred because the Sn-sn pair of alleles were probably also
segregating in this cross (JI1420 appears to carry Sn while NEU3 carries
sn) (see 3). This would also explain the variability within these groups
and the poor separation between the dwarf (LkLvle) and taller (Lklvle) plants (see 3).
The overall F2 segregation of 16 erectoides, 44 dwarf and 17 taller
plants (Fig. 1) is in agreement with both a 3:9:4 and 4:9:3 segregation ratio (c22
= 0.4 and 1.0, respectively). In the F3, the erectoides class bred
true (6 progeny from each of 6 F2 plants) while of the 4 "tall" F2
plants tested in F3 (12 progeny per F2 plant), one
segregated to give 3 erectoides and 9 "tall" plants. Consequently it appears
that gene lk is epistatic to the gene lv and genotype lk
lv (on a lebackground) possesses an erectoides phenotype. The
mean length between nodes 4 and 6 was 1.40 ± 0.15 cm (n=3) for the lk
lv F3 segregates. This was slightly longer than the overall mean
for F3 progeny from a selection of erectoides (lk) F2
segregates (1.03 ± 0.06 cm, n=12).

The results suggest that the GA-non-responsive character
conferred by lk over-rides the GA-hyper-responsive character conferred by
lvto cause genotype lklv to possess an
erectoides phenotype. However, lv may still exert some small quantitative
effect within this erectoides group comparable with that caused by the slender
gene combination (lacryS) (see 2).